Ablation catheters typically have a tip electrode at their distal end for ablating the heart tissue. Temperature sensors are used to monitor the temperature of the tip electrode in contact with the heart tissue to assist the physician in determining whether the tip electrode is too hot. When the tip electrode becomes too hot, coagulation forms on the tip electrode, causing a steam explosion in the heart tissue. Typical tip electrodes have a length of approximately 4 mm. In certain applications, e.g., when longer lesions are desired, longer tip electrodes are preferred. When longer tip electrodes are used, e.g., around 8 mm to 12 mm, accurately determining the temperature of the electrode in contact with the heart tissue becomes more difficult. This is because the temperature of the tip electrode will vary across its surface, e.g., depending on whether the surface is in contact with myocardium or circulating blood. Consequently, if a single temperature sensor is used, it may be at a location within the tip electrode remote from the portion of the tip electrode in contact with the heart tissue. If that sensor is adjacent a portion of the tip electrode in contact with rapidly circulating blood, it may provide a temperature reading which is not indicative of the portion of the tip electrode that is in contact with the heart tissue. Thus, it is desirable to place multiple temperature sensors along the length of the tip electrode to more accurately monitor the temperature of the portion of the tip electrode in contact with the heart tissue.
Preferably, the temperature sensor will be as close as possible to the surface of the tip electrode in contact with the heart tissue. However, placement of a temperature sensor on one side of the tip electrode will provide erroneous temperature readings if the opposite side of the electrode is in contact with the heart tissue. Therefore, it is generally preferred that temperature sensors be located along the axis of the tip electrode.
The temperature of the tip electrode is typically controlled by an RF generator having a feedback control circuit. The generator receives signals from the temperature sensor and supplies more or less RF energy to the tip electrode depending on the signal received. When multiple temperature sensors are used, the generator uses as a control the temperature sensor measuring the fastest temperature change.
To take advantage of multiple temperature sensors, it is desirable to know the distance between the sensors within the tip electrode. This allows the physician to have a general idea of the region of the tip electrode that each sensor is measuring. However, it is difficult to place multiple sensors within the tip electrode at known locations. Typically, temperature sensors are soldered or glued directly into holes within the tip electrode. Because of the size of the components, it is difficult to attach a temperature sensor within a hole at a particular location using this traditional method. Thus, a need exists for a catheter having multiple temperature sensors within the tip electrode situated at predetermined spaced-apart locations.